144 



HYDROIDA II 



The gonothecse are set on the upper side of the branches. They are pear-shaped, with rudi- 

 mentary neck and broad aperture. 



Material : 



"Ingolf" St. 31 66°35' N., 55°54' W., depth 88 fathoms i,6° 

 - 34 65-17' N, 54 °i 7 ' W, - 55 - 



Greenland: Davis Strait, — 100 — (without further details) |type specinienl. 



Iceland: Skagi, 20 — [labelled Tliajaria lonchitis\ 



Dyrafjord, 15 — 



In all probability, this species also will prove to have a pinnate development stage, like the 

 other, spiral Thujaria species. In the arrangement of the hydrothecse, Thujaria alternitheca forms a 

 parallel to Abietinaria (?) fuse -a (Johnston), and it is interesting here to note how the hydro thecae, 

 owing to their extremely close accumulation, thrust their opening part to one side or the other from 

 the base of the next following. An investigation of the tip of the branch shows that this is a secon- 

 dary phenomenon. The hydrothecse are to begin with symmetrically situate, with their symmetrical 

 plane parallel to the branch axis; only on the formation of a new distal hydrotheca is the aperture 

 of the one behind it thrust out to the side. We have here, then, a typical instance of convergency, 

 as towards A bictinaria (?)fusca, which cannot be taken as evidence of closer relationship, and thus does 

 not afford any justification for uniting the two species mentioned, and other multiserial forms in a 

 special genus Selaginopsis; any such would also have to include species with and those without blind 

 sack, which can hardly be considered permissible. 



600 m. ._ tooo m. 



Fig. LXXVIII. Finds of Thujaria alternitheca. 



